Fluid tight annular seals

ABSTRACT

A fluid seal of the O-ring type in which extrusion of the O-ring along the leakage path when under pressure is prevented by means of a support ring of bow-shaped cross-section on the downstream side of the O-ring between the O-ring and an abutment surface.

United States Patent Grime et al.

[151 3,687,465 1 Aug. 29, 1972 [54] FLUID TIGHT ANNULAR SEALS [72]Inventors: Frank L. Grime, Coventry; Arthur Downs, Kenilworth, both ofEngland [73] Assignee: Keelavite Hydraulics Limited [22] Filed: Jan.9,1970 [21] Appl.No.: 1,831

30] Foreign Application Priority Data OTHER PUBLICATIONS The Journal ofTeflon Vol. 5 No. 4 May 1964 page 7 Slipper Seals: O-Rings with TeflonFor Low Wear New York R. E. Holfman Pn'mary Examiner-William F. ODeaAssistant Examiner-Robert J. Smith I Attorney-Watson, Cole, Grindle &Watson [57] ABSTRACT A fluid seal of the O-ring type in which extrusionof the. O-ring along the leakage path when under pressure is preventedby means of a support ring of bowshaped cross-section on the downstreamside of the O- ring between the O-ringand an abutment surface.

v 7Claims,2Dra'wingFigures Jan. 10,1969 Great Britain 1735/69 [52] U.S.Cl ..277/188, 277/177 [51] Int. Cl. ..F16j 15/10 [58] Field of Search..277/123, 124, 165, 58, 177,

[56] References Cited 7 UNITED STATES PATENTS 2,494,598 1/ 1950 Waring..277/188 2,705,177 3/ 1955 Waring ..277/188 3,375,016 3/ 1968 Jellineket a1 ..-277/58 2,760,794 8/1956 Hartranft ..'....277/ 165 FLUID TIGHTANNULAR SEALS This invention relates to fluid tight annular seals of thekind afi'orded by O-rings. Such seals are employed, for example, in pipecouplings but are also used in other locations where an annular leakagepath is to be sealed.

By an O-ring is to be understood a ring which is usually but notnecessarily of circular cross-section and which is made of rubber orother deformable resilient material and which is pressed up against anabutment wall, such as a shoulder, which reduces the cross-section ofthe path by the fluid pressure acting on one side of the ring to deformthe ring and cause it to expand in directions generally perpendicular tothe direction in which pressure is applied to it so as to seal againstthe two opposite surfaces between which it is positioned so as toprevent the-escape of fluid past the O-ring along the annular leakagepath.

When the cross-section of the O-ring or of the support ring (hereafterreferred to) is mentioned, the term refers to one of the two sectionsproduced by-a section plane containing (assuming the case of a circularring) the axis of generation of the ring.

A problem with O-ring seals is that the pressure acting on one side ofthe ring tends to force the ring against the abutment wall and into thenarrow annular passage which must exist on at least one of the inner andouter boundaries of the abutment wall. This may be described as atendency for the O-ring to be extruded into the narrow annular passage.Such extrusion 7 may of itself impair the integrity of the seal and mayalso damage the O-ring and'so give rise to imperfect sealing after theseal has been in use for'some time. This is particularly the case if thepressure differences experienced are high and/or fluctuating. Thetendency for extrusion to occur is clearly related to the breadth Thenominal external diameters of such pipes normally have quite widetolerances. Not only may variations in the dimensions of one or bothcomponents affording the surfaces defining the narrow annular passageaffect the size of the narrow annular passage but they may also affectthe distance between the two opposite surfaces of the part of theannular leakage path against which the O-ring bears to effect a seal.

it has already been proposed in U.S.. Pat. No. 2,456,356, issued Dec.14, 1948 to L8. Aber, to provide a restraining ring of the same materialas the O- ring and positioned alongside the O-ring between the O-ringand an abutment wall afforded by the side of the groove in which theO-ring and the restrain ng ing are positioned. Various cross-sections ofrestraining rings are shown but in each case the surface against theabutment surface is flat. With this arrangement only a small part of therestraining ring is able to distort when pressure is applied so thatthis arrangement is only suitable where the dimensional tolerances ofthev parts to be sealed are very closely controlled. Another arrangementused as a dynamic seal is disclosed in US. Pat.

No. 2,494,598 issued Jan. 13, 1950 to A.C. Waring. In this arrangement arubber ring of circular cross-section bears against a shoulder on apiston. The shoulder is semi-circularly grooved to face the directionfrom which the pressure is to come. Between the shoulder and the rubberring is a ring of polytetrafluoroethylene which is of arcuatecross-section so as to seat in the groove in the shoulder. When the sealis under pressure the lip formed by the outer edge of the arcuate ringis distorted into contact with the cylinder wall surrounding the piston.Here again, only a small part of the second ring is able to' distort sothat the tolerances must be very tight if the second ring is to functionsatisfactorily.

It is an object of the present invention to provide a seal assemblycomprising an Orring and a second ring which will operate satisfactorilyover a wide dimensional tolerance range.

This object is achieved, according to the present invention, byconstructing the surface of the support ring on theside adjacent theabutment wall and the surface of the abutment wall such that the supportring makes contact with the abutment wall only in a narrow annularregion intermediate the radially inner and radially outer circumferencesof the support ring.

Such a seal assembly operates in the following. manner. When pressure isapplied to the O-ring it deforms by decreasing its axial dimension andincreasing its radial dimension in the usual way. It also presses thesupport ring against the abutment wall. The pressure of the O-ring onthe concave surface of the support ring tends to open out the concavitythus closing the clearances between the support ring and the sur-- facesagainst which the O-ring seals. Thus extrusion of the O-ring isresisted. Since the support ring is in contact with the abutmentwallonly in a narrow annular.

v radially intermediate region, the whole cross-section of the supportring is free to deform that is to say, the cross-section of they supportring may be thought of as two cantilevers fixed at the central regionwhere the support ring contacts the abutment wall and the radially innerand outer edges of the ring are free from the bow further apart.Preferably the radius of curva-- ture of the central portion of theconcave surface of the support ring is slightly smaller than that of theO-ring, for example of the order of 5 to 10 percent smaller, so that inthe undistorted condition the support ring will contact the O-ring attwo regions which are radially spaced from one another on either side ofthe-portion having the smaller radius of curvature and of the narrowannular region of contact of the support ring with the abutment wall asclearly shown in FIG. 2. The two rings may be stuck together in theseregions of contact to form a single composite component for ease ofhandling and installation.

Since the whole cross-section of the support ring takes part in thedeformation under pressure,,it is possible to arrange for the relativemovement apart of the radially inner and outer edges of the support ringto be considerable. This is of particular value where considerablevariations in the dimensions of the annular leakage path are to beexpected. Seal assemblies according to the present invention aretherefore valuable when at least one of the relevant surfaces isunmachined as by being afforded by a pipe. However, they may also beuseful where all the relevant surfaces are machined as they may make itpossible to impose less rigorous tolerances on the finished dimensionsof these surfaces.

The material of which the support ring is formed and/or its constructionwill usually be such that it will not itself act as a sealing ringpreventing the flow of fluid under pressure past it and hence throughthe narrow annular passage referred to, the criterion being that, whenthe O-ring is under fluid pressure, the support ring should be sodeformed by the action of the O- ring on it as to ensure that eitherthere are no clearances between it and the opposite surfaces againstwhich the O-ring seals or that such clearances are smaller than thoseinto which the O-ring can be extruded to any appreciable degree by thatpressure.

- ternally screw-threaded end portion 2 and a bore com.-

prising an inner part 3 of a diameter such as to receive the end of apipe 4 with a free but relatively close fit, an intennediate part 5 ofsubstantially cylindrical form and substantially larger diameter thanthe pipe 4 to form an annular space to receive a sealing ring 6 of theO.-ring type and with a shoulder 7 between the parts 3 and 5, and anouter tapered part 8. Co-operating with the tubular coupling member 1 isa clamping member in' the form of a ring nut 9 having a portion with aninternal screw-thread 10 co-operating with the screwthreaded part 2 ofthe tubular member 1, and a portion A suitable material for the supportring is nylon, particularly Nylon ll, or other moulded plastics materialhaving sufficient rigidity not itself to be extruded into i coupling,when not subject to pressure,.followed by reassembly of the same partswith the same ease as the original assembly.

The invention is particularly applicable to pipe couplings comprising atubular coupling member which has a bore into which the end portion ofthe pipe is to be inserted, the seal to be established between the,

coupling member and the pipe. The coupling member includes an inner partof relatively small diameter. to receive the end of the pipe and anadjacent part which is of larger diameter than the inner part,terminates at its junction with the inner part at an annular shoulderhaving an internal circumferential surface 1 l of frustoconical formwith its largest diameter adjacent to the tubular member 1. A splitcollet 12, which has a frustoconical outer surface is arranged to liewithin and to cooperate with the frusto-conical bore 11 and isformedintemally with a series of serrations indicated at 13, which,- inthe assembled joint, grip the pipe 4 as shown.

Projecting into the space constituted by the part 5 of the bore of thetubular coupling member 1 and the ad- 3 5 jacent part of the pipe 4 is adistance piece 14 of annuand forms with the part of the pipe which itsurrounds, the annular shoulder, and an annular distance piece whichenters the open end of the bore freely and itself freely surrounds thepipe an annular space in which an O-ring lies and is retained by saiddistance piece. In such a pipe coupling the support ring is placedbetween the O-ring and the end of the annular distance An example ofsuch a pipe coupling is described andillustrated'in the specification ofCanadian Pat. No; 793,808. The present invention may be applied to sucha pipe coupling by adding asupport ring constructed and arranged in themanner described above.

lar form comprising a cylindrical portion 15 having a plane end face 15aand an external flange 16 at one end of the cylindrical portion. Thedistance piece has a bore through which'the. pipe 4 passes'freely'butwith relatively small clearance, the-end of the cylindrical portion 15adjacent to the O-ring 6 also lying freely but with a small clearancewithin the part 5 of thebore of the tubular coupling member 1. i

Pressurized fluid from the pipeenters the annular f space 20 through theannular clearance space 21 between the pipe and the tubular couplingmember 1.

The O-ring prevents fluid escaping from the annular space 20 through thenarrow annular passages 22 and 23 between, on the one hand, the distancepiece 14 and, on the other hand,"the tubular coupling member 1 and thepipe 4 respectively. v Interposed between the O-ring 6 and the adjacentend of the distance piece 14 is a support ring 17 formed of nylon orsimilar material and having in its undistorted state a bow-shapedcross-section as shown in FIG. 2. The central part of the section isbounded by circular arcs 24, 25 'while the outer parts are formed bysmall clearance between its inner circumference and the outercircumference of the pipe 4. During the period of assembly when thesupport ring 17 and the O- ring 4 are being pushed by the distance piece14 into posiu'on within the annular space in which they are to lie, thesupport ring 17 can move freely into the position in which the centralregion 30 of its convex surface abuts the plane end wall 15a of thedistance piece 14. When, after assembly, fluid pressure from within thepipe 4 acts in normal manner upon the O-ring 6 to apply pressure to itin the direction indicated by the arrows in FIG. 2the support ring 17will be distorted by the force applied to it by the O-ring 6 so that thearms of the bow constituting its cross-sectional form will be opened outto bring the outer ends of these arms into engagement or close proximitywith the surfaces respectively of the part 5 of the bore of the tubularcoupling member 1 and the external circumference of the pipe 4. Thenarrow passages 22, 23 through which the O-ring might otherwise bepartially extruded by fluid pressure are either reduced or eliminated insuch a manner that no such extrusion occurs.

What we claim as our invention and desire to secure by by Letters Patentis:

l. A seal assembly comprising an annular leakage path to be sealed, thepath being defined by at least annular outer and inner walls and anabutment wall which reduces the cross-section of the path, an O-ring inthe path upstream of the abutment wall in the direction of leakagesealing engaging said annular walls, and a deformable support ringbetween the O-ring and the abutment wall, the support ring having agenerally concave surface on the side adjacent the O-ring, the radius ofcurvature of the central portion of the concave surface of the supportring being slightly smaller than that of the adjacent surface of theO-ring, the surface of the support ring on the side adjacent theabutment wall and the surface of the abutment wall being such that thesupport ring makes contact with the abutment wall only in a narrowannular region intermediate the radially inner and radially outercircumferences of the support ring and the O-ring contacting the supportring in two regions which are radially inward and outward of said narrowannular region whereby pressure applied to the side of the O-ring remotefrom the support ring causes the radially inner and outer circumferencesof the support ring to be bowed outwardly thereof so as to preventextrusion of the O-ring past the support ring.

2. An assembly as claimed in claim 1 in which the abutment wall extendsin a plane nonnal to the axis of the annular leakage path and of theO-ring and support ring.

3. An assembly as claimed in claim 1 in which the surface of the supportring adjacent the abutment wall is curved and is convex.

4. An assembly as claimed in claim 3 in which the surface of the supportring adjacent the abutment wall is approximately parallel withtheconcave surface.

5. A seal assembly as claimed in claim 1 in which the support ring ispermanently secured to the O-ring.

6. A seal assembly comprising an annular path to be sealed, the pathbeing defined by at least annular outer and inner walls and an abutmentwall which reduces the cross-section of the path, an O-ring disposed inthe ath u stream of said abutment wall in the directi f eakag sealingengaging said annular walls, a d a deformable support ring disposedbetween said O-ring and said abutment wall, said support ring having agenerally concave surface on its side adjacent said 0- ring, the radiusof curvature of the central portion of the concave surface of thesupport being slightly smaller than that of the adjacent surface of theO-ring, and said support ring further having radially inner and radiallyouter circumferential walls respectively spaced a slight distance fromsaid'outer and inner walls in the relaxed condition of said supportring, the surface of said support ring on its side adjacent saidabutment wall and the surface of said abutment wall being such that saidsupport ring makes contact with said abutment wall only in a narrowannular region thereof in its relaxed condition intermediate saidradially-inner and radially outer circumferential walls and the O-ringcontacting the support ring in two regions which are radially inward'andoutward of said narrow annular region, whereby pressure applied to theside of said O-ring remote from said support ring causes said radiallyinner and outer circumferential walls to be bowed into contact,respectively, with said annular inner 'and outer walls so as to preventextrusion of said O-ring past said support ring.

7. A seal assembly as claimed in claim 6 in which the support ring ispermanently secured to the O-ring.-

1. A seal assembly comprising an annular leakage path to be sealed, thepath being defined by at least annular outer and inner walls and anabutment wall which reduces the cross-section of the path, an O-ring inthe path upstream of the abutment wall in the direction of leakagesealing engaging said annular walls, and a deformable support ringbetween the O-ring and the abutment wall, the support ring having agenerally concave surface on the side adjacent the O-ring, the radius ofcurvature of the central portion of the concave surface of the supportring being slightly smaller than that of the adjacent surface of theO-ring, the surface of the support ring on the side adjacent theabutment wall and the surface of the abutment wall being such that thesupport ring makes contact with the abutment wall only in a narrowannular region intermediate the radially inner and radially outercircumferences of the support ring and the O-ring contacting the supportring in two regions which are radially inward and outward of said narrowannular region whereby pressure applied to the side of the O-ring remotefrom the support ring causes the radially inner and outer circumferencesof the support ring to be bowed outwardly thereof so as to preventextrusion of the O-ring past the support ring.
 2. An assembly as claimedin claim 1 in which the abutment wall extends in a plane normal to theaxis of the annular leakage path and of the O-ring and support ring. 3.An assembly as claimed in claim 1 in which the surface of the supportring adjacent the abutment wall is curved and is convex.
 4. An assemblyas claimed in claim 3 in which the surface of the support ring adjacentthe abutment wall is approximately parallel with the concave surface. 5.A seal assembly as claimed in claim 1 in which the support ring ispermanently secured to the O-ring.
 6. A seal assembly comprising anannular path to be sealed, the path being defined by at least annularouter and inner walls and an abutment wall which reduces thecross-section of the path, an O-ring disposed in the path upstream ofsaid abutment wall in the direction of leakage sealing engaging saidannular walls, and a deformable support ring disposed between saidO-ring and said abutment wall, said support ring having a generallyconcave surface on its side adjacent said O-ring, the radius ofcurvature of the central portion of the concave surface of the supportbeing slightly smaller than that of the adjacent surface of the O-ring,and said support ring further having radially inner and radially outercircumferential walls respectively spaced a slight distance from saidouter and inner walls in the relaxed condition of said support ring, thesurface of said support ring on its side adjacent said abutment wall andthe surface of said abutment wall being such that said support ringmakes contact with said abutment wall only in a narrow annular regionthereof in its relaxed condition intermediate said radially inner andradially outer circumferential walls and the O-ring contacting thesupport ring in two regions which are radially inward and outward ofsaid narrow annular region, whereby pressure applied to the side of saidO-ring remote from said support ring causes said radially inner andouter circumferential walls to be bowed into contact, respectively, withsaid annular inner and outer walls so as to prevent extrusion of saidO-ring past said support ring.
 7. A seal assembly as claimed in claim 6in which the support ring is permanently secured to the O-ring.